In marking inks or text markers, water-soluble dyes that fluoresce in the alkaline environment are used customarily. Such a dye is, for example, described in the German patent DE-PS 23 15 680 (hydroxypyrenetrisulfonic acid (Solvent Green 7 C.I. 59040)). This dye, which is also referred to as pyranine, can be used to highlight certain passages in texts clearly by painting over them. The fluid exhibits the advantage that the marking that is produced with it on a substrate is color intensive because of its day-glow paint-like character. Beyond that, the coloring effect occurs immediately after its application. One disadvantage of these inks, however, may be seen in their inadequate resistance to light. In the published German patent application DE-OS 24 41 823, it is suggested that the oxidative bleaching of the dyes, caused by the oxygen in the air, be eliminated by means of substances that have a reducing effect. DE 40 20 900 C1 is the source of marking fluids that contain saccharose, lactose, maltose, or monosaccharides that are derived from them. An improvement of photo-resistance is said to be achieved as a result of this measure. What has proven to be problematical in conjunction with this solution, however, is that the marker inks that are applied to paper quite quickly assume a brown color. This might be due to the fact that saccharose crystals that form are separated from the dye, and therefore, they no longer surround the dye in a protective manner.
The technical problem that underlies the present invention thus resides in providing marking fluids and methods for their manufacture that assure improved light-fastness and luminosity of the marker substance that is present in the fluid without the occurrence of color deteriorations after the marking fluid is applied to substrates.